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Evidence of Evolution Chapter 17 Impacts, Issues Measuring Time Evidence of events that happened millions of years ago – such as meteor impacts – lead to inferences about evolution of life on Earth 17.1 Early Beliefs, Confounding Discoveries Belief systems are influenced by the extent of our knowledge Beliefs that are inconsistent with systematic observations of the natural world tend to change over time Naturalists and Biogeography Aristotle was one of first naturalists – people who observe life from a scientific perspective In the late 1800s, Alfred Wallace and others were pioneers in biogeography – the study of patterns in the observation of species Patterns in Biogeography Comparative Morphology Comparative morphologists study body plans and structures among groups of organisms • Some organisms are outwardly similar, but different internally; others differ outwardly, but have similar internal structures • Some organisms have vestigial parts with no apparent function Vestigial Body Parts coccyx limb bud Fig. 17-3, p. 261 Geology Geologists found identical sequences of rock layers in different parts of the world • Different layers held different fossils – evidence of earlier forms of life Cumulative findings from biogeography, comparative morphology, and geology led to new ways of thinking about the natural world Fossils 17.2 A Flurry of New Theories By the 1800s, many scholars realized that life on Earth had changed over time, and began to think about what could have caused the changes New Evidence and Old Beliefs Catastrophism • Georges Cuvier proposed that many species that once existed became extinct due to catastrophic geological events unlike those known today Gradualism • Jean-Baptiste Lamarck proposed that individuals changed in response to their environment, and passed those changes on to their descendents Reconsidering Old Beliefs Theory of uniformity • Lyell’s book, Principles of Geology, proposed that gradual, repetitive geological processes shaped the Earth over great spans of time • Lyell’s insights shaped Charles Darwin’s thinking during his five-year voyage on the Beagle Voyage of the Beagle Darwin observed unusual fossils and diverse species in a range of habitats Beagle and The Galapagos Islands 17.1-17.2 Key Concepts Emergence of Evolutionary Thought Long ago, naturalists started to catalog previously unknown species and think about the global distribution of all species They discovered similarities and differences among major groups, including those represented as fossils in layers of sedimentary rock 17.3 Darwin and Natural Selection Darwin’s observations of species in different parts of the world helped him understand a driving force of evolution – natural selection Old Bones and Armadillos Darwin observed similarities between fossil glyptodons in Argentina and the armadillo A Key Insight – Variation in Traits Darwin’s observations: • Populations can produce more individuals than their environment can support • Some versions of a trait might enhance an individual’s ability to survive and reproduce in its particular environment • Example: Finches in the Galapagos Islands Finches in the Galapagos Islands Natural Selection Natural selection • Differential survival and reproduction among individuals of a population that vary in details of shared, inherited traits Adaptive trait • Any trait that enhances an individual’s fitness (ability to survive and reproduce in a particular environment) Principles of Natural Selection Stepped Art Table 17-1, p. 265 17.4 Great Minds Think Alike Darwin’s insights into evolution were made possible by contributions of scientists who preceded him Alfred Wallace independently developed the idea of evolution by natural selection Alfred Wallace Wallace drew on his own observations of plant and animal species and proposed that natural selection is a driving force of evolution 17.3-17.4 Key Concepts A Theory Takes Form Evidence of evolution, or changes in lines of descent, gradually accumulated Charles Darwin and Alfred Wallace independently developed a theory of natural selection to explain how heritable traits that define each species evolve 17.5 About Fossils Fossils are remnants or traces of organisms that lived in the past They give us clues about evolutionary relationships The fossil record will always be incomplete Fossils Fossils • Remains of bones, teeth, shells, seeds, spores, or other body parts Trace fossils • Evidence of an organism’s activities (nests, trails, footprints, burrows, bore holes, eggshells, feces) Fossils Fig. 17-9a, p. 267 Fig. 17-9b, p. 267 Fig. 17-9c, p. 267 How Do Fossils Form? Organisms or traces are covered in sediments or volcanic ash Inorganic compounds dissolved in water slowly replace minerals in bones and hard tissues Pressure and mineralization transform remains into rocks Fossil-Containing Sedimentary Rock The oldest fossils are usually in the deepest layers of sedimentary rocks The Fossil Record The fossil record will never be complete • Geologic events obliterated much of it • Slanted toward species with hard parts, dense populations, wide distribution, long periods of time • Substantial enough to help reconstruct patterns and trends in the history of life, and establish some lines of descent (lineages) 17.6 Dating Pieces of the Puzzle Researchers use predictable radioisotope decay to estimate the age of rocks and fossils Radiometric dating • Reveals the age of a material by determining its radioisotope and daughter element content Radioisotopes Radioisotope • A form of an element with an unstable nucleus • Decays into atoms of another element • Example: uranium 238 → lead 206 Half-life • The time it takes for half of a radioisotope’s atoms to decay into a daughter element Half-Life parent isotope daughter isotope newly formed rock after one half-life after two half-lives Fig. 17-11, p. 268 parent isotope daughter isotope newly formed rock after one half-life after two half-lives Stepped Art Fig. 17-11, p. 268 Animation: Radioisotope decay Carbon 14 Dating Animation: Radiometric dating 17.7 A Whale of a Story New fossil discoveries are continually filling the gaps in our understanding of the ancient history of many lineages New Links in the Ancient Lineage of Whales New Links in the Ancient Lineage of Whales New Links in the Ancient Lineage of Whales 17.5-17.7 Key Concepts Evidence From Fossils The fossil record offers physical evidence of past changes in lines of descent We use the property of radioisotope decay to determine the age of rocks and fossils 17.8 Putting Time into Perspective Geologic time scale • The chronology of Earth’s history • Measured by radiometric dating and fossils in similar sequences of sedimentary rock layers around the world The Geologic Time Scale Fig. 17-14a, p. 270 Fig. 17-14b, p. 271 Animation: Geologic time scale 17.9 Drifting Continents, Changing Seas For billions of years, slow movements of Earth’s outer layer and catastrophic events have changed the land, atmosphere, and oceans, with profound effects on the evolution of life Continental Drift Continental drift • All continents were once part of a supercontinent – Pangea – that split and drifted apart • Evidence: Magnetic rocks Plate tectonics • The mechanisms of continental drift • Plate grow from ridges and sink into trenches Plate Tectonics trench A A Plumes of molten rock rupture a tectonic plate at what are called “hot spots.” The Hawaiian Archipelago has been forming this way. hot spot ridge B B At oceanic ridges, huge plumes of molten rock welling up from Earth’s interior drive the movement of tectonic plates. New crust spreads laterally as it forms on the surface, forcing adjacent tectonic plates away from the ridge and into trenches elsewhere. trench C C At trenches, the advancing edge of one plate plows under an adjacent plate and buckles it. The Cascades, Andes, and other great coastal mountain ranges formed this way. rift D D At rifts, continents rupture in their interior as plates slide apart from each other. Fig. 17-15, p. 272 Boundaries of Tectonic Plates San Andreas Fault Gondwana Supercontinents continually form and split, altering habitats and influencing evolution Gondwana • Ancient supercontinent, older than Pangea • Similar fossils and geologic formations in Africa, India, South America and Australia The Drifting Continents A 420 mya B 237 mya C 152 mya D 65.5 mya E 14 mya Fig. 17-17, p. 273 Fig. 17-17 (top left), p. 273 Fig. 17-17 (top right), p. 273 17.8-17.9 Key Concepts Evidence From Biogeography Correlating evolutionary theories with geologic history helps explain the distribution of species, past and present Animation: Comparative pelvic anatomy Animation: Continental drift Animation: Finches of the Galapagos Animation: Geologic forces Animation: Plate margins Animation: The Galapagos Islands ABC video: Creation vs. Evolution ABC video: Chickens have a new ancestor ABC video: Indonesian Earthquake ABC video: Asteroid Menace Video: Measuring time